This invention relates to processes for producing aromatic ethers. It more specifically relates to the vapor phase production of aromatic ethers from phenols. Aromatic ethers are useful reactants and solvents, heat-transfer media and herbicides.
Williamson's ether synthesis is a well-known process for the manufacture of ethers. Williamson's ether synthesis can be the liquid phase reaction of a sodium phenoxide and an alkyl halide to form an alkyl, phenyl ether and sodium halide salt. See Morrison, R. T., et al., Organic Chemistry, 3rd ed, p. 556 (1975). This process disadvantageously consumes stoichiometric amounts of NaOH (to generate the sodium phenoxide) and disadvantageously produces a stoichiometric amount of a sodium halide salt by-product (which converts the high value halide reactant to a low value product).
Alternate processes which do not form unacceptable by-products are also known. Direct alkylation of phenols by treatment with diazomethane, tetramethoxymethane or pentamethoxyphosphorane, have been previously disclosed in the art. Other processes involve treating phenol with methanol in the presence of dicyclohexylcarbodiimide or a mixture of diethylazodicarboxylate and triphenylphosphine. These processes have proven to be rather inefficient, uneconomical or ecologically unsuitable.
Soviet Pat. No. 276,014, issued to I. I. Yukel'son et al. teaches that a catalyst containing the mixture of 45-55 percent Cr.sub.2 O.sub.3, 25-30 percent Fe.sub.2 O.sub.3 and 20-25 percent ZnO catalyzes the liquid phase alkylation of phenol and t-butyl chloride to alkyl phenols at over 98 percent yield. Most of the product is dialkylated. This reaction does not produce ethers.
It would be desirable to have a process that converted aromatic alcohols to ethers without consuming a stoichiometric amount of a catalyst and without generating a stoichiometric amount of a halide salt.